The rotors of synchronous electric motors are used in household appliances, such as refrigerators, freezers, air conditioners, hermetic compressors, laundry machines, pumps, fans, etc.
Such motors are usually formed by a stator, a rotor and permanent magnets, said rotor being of the type formed by a rotor core, which carries the permanent magnets, and a rotor cage usually made of aluminum and formed by end rings connected to aluminum axial bars formed during a casting process of said rotor cage.
The rotor core includes a stack of superposed annular steel laminations provided with openings longitudinally aligned with the openings of the other laminations of the stack so as to define a plurality of axial channels interconnecting the external faces of the end laminations of the stack and which are angularly spaced apart along a circular alignment concentric to the longitudinal axis of the lamination stack, but radially spaced back in relation to a circumferential alignment of peripheral housings to be filled with a forming material of the rotor cage during the casting process of the latter, forming the axial bars thereof.
The rotor cage presents, adjacent to each end of the rotor core, an end ring, or short-circuit ring, which generally restrains, directly or indirectly the permanent magnets from being axially displaced out from the magnet housings of the rotor.
In a known solution disclosed in WO 01/06624, the axial retention of the permanent magnets is achieved by providing an end cap closing each end of the rotor core and onto which is seated at least one inner peripheral portion of an adjacent end ring of the rotor cage. While this solution avoids the involuntary escape of each permanent magnet in relation to its respective housing, it presents some inconveniences such as high cost and loss of efficiency when the end caps are made of electric steel, for example.